1. Field of the Invention
The present invention relates to reciprocating pumps, such as pumps of the duplex or triplex type and, more specifically, to liners for use in such pumps.
2. Description of the Prior Art
In certain applications, corrosive or abrasive fluids (for example, oil well drilling fluid, commonly known as "mud"), must be pumped. Pumps used in these applications are reciprocating pumps typically of the duplex or triplex type provided with two or three cylinders, as the case may be, a piston being reciprocally disposed in each cylinder. Each cylinder communicates with a suction and discharge valve equipped chamber so that, as the piston is reciprocated by the piston rod, drilling fluid will be ultimately drawn into and discharged from the working chambers. Since the material pumped is of an abrasive character, and frequently corrosive as well, wear on the piston and cylinder wall is quite severe, and it has been common practice, in order to more easily repair a worn pump, to provide each cylinder with a replaceable steel liner that reciprocably supports the piston in the cylinder. Nevertheless, the abrasive fluid--e.g., mud--results in a relatively short lifetime of the liner and the piston, necessitating frequent replacement. It will be apparent that because of the abrasive nature of the fluids being pumped, the liner must have a hard interior surface. Additionally, because the pressures and forces that act on the liner are extreme, the liner is typically quite large and heavy.
Attempts to address the issue of making a liner that resists abrasion and corrosion and that is economical are numerous. As illustrated in U.S. Pat. No. 5,617,773, incorporated herein by reference for all purposes, the industry has generally settled on a dual-metal pump liner having an abrasive and corrosive-resistant inner sleeve and a machinable outer shell. One such liner is centrifugally cast, wherein a carbon steel outer shell is cast on the spinning mold and a high-chrome steel is then poured into the interior of a hot outer shell. Upon cooling, the result is a metallurgical bond between the inner sleeve and the outer shell, and the liner has a hard inner surface and a machinable outer surface. However, critical spinning speeds, pour temperatures, and other parameters make such a liner process expensive and the liners difficult to make. Another method that has been used in the manufacturing of liners is a shrink fit, wherein the carbon steel shell is heated and the high chrome sleeve is cooled. The two are then press-fitted together. Upon reaching a common temperature, the sleeve has expanded and the shell has shrunk, thus creating a tight fit. Still other attempts have been made at static casting the steel shell in the sleeve; however, that method was abandoned as a failure because the brittle sleeve tended to crack.
Thus, there remains a need for a pump liner that is corrosion- and abrasion-resistant, that can withstand the pressures and forces exerted on the liner, and that is lightweight to permit easier field installation.